Many liquid crystal pixel units are provided in a liquid crystal display device of VA (Vertical Alignment) mode, each liquid crystal pixel unit corresponds to a smallest display point, which can be individually controlled, on the display screen, that is, each liquid crystal pixel unit corresponds a sub-pixel. In each liquid crystal pixel unit, the liquid crystal molecules will be driven to be inclined toward certain directions (orientations) from vertical arrangements (i.e., perpendicular to the surface of the display panel). The filtering capability of a liquid crystal layer is determined by the angles between the liquid crystal molecules and lights. Thus, if all the liquid crystal molecules in a liquid crystal pixel unit take a same direction (the same orientation/inclination angle), the liquid crystal pixel unit renders varied brightness when viewed from different positions; in other words, lights emitted from the liquid crystal pixel unit to different positions have different directions, and therefore have different angles with the liquid crystal molecules), the display quality is affected.
Practically, each liquid crystal pixel unit is divided into a plurality of domains, the directions of the liquid crystal molecules within each domain are the same, and the directions of the liquid crystal molecules among different domains are different (i.e. have different orientations/inclination angles). The brightness difference of the liquid crystal pixel unit viewed from different locations may be reduced by an average effect of the domains. The liquid crystal pixel unit may divided into domains in two different ways: firstly, the orientations of the liquid crystal molecules may be altered (i.e. setting a plurality of “orientation domains”), which can be implemented by setting convexity or different alignment layers, or by changing shapes of the pixel electrodes; secondly, a plurality of pixel electrodes applied with different voltages may be provided in each liquid crystal pixel unit (i.e. the content of a sub-pixel is displayed using the plurality of pixel electrodes), such that the inclination angles of the liquid crystal molecules corresponding to different pixel electrodes are different from each other. These two ways can be combined, for example in a liquid crystal display device of SPVA (Super Patterned Vertical Alignment) mode, a plurality of pixel electrodes are provided for each liquid crystal pixel unit, and each pixel electrode corresponds to several orientation domains.
A CS-SPVA mode liquid crystal display device using CS (charge share) technology is proposed for controlling the voltage of each pixel electrodes in the liquid crystal pixel unit. As shown in FIG. 1, a low-voltage pixel electrode 11 and a high-voltage pixel electrode 12 are provided in each liquid crystal pixel unit of CS-SPVA mode, the two pixel electrodes 11 and 12 are connected with a data line Data respectively through charging TFT TC1, TC2 which are controlled by a charging gate line GC; the low-voltage pixel electrode 11 is also connected to the source of a first shared TFT TS which is controlled by a shared gate line GS, the drain of the first shared TFT TS is connected to one end of a first shared capacitor CS1, the other end of the first shared capacitor CS1 is connected with a common electrode line Com. As shown in FIG. 2, when a display period (frame) of the liquid crystal pixel unit is initiated, the charging gate line GC provides a charging connection signal, the two pixel electrodes 11 and 12 are charged to a same voltage through the data line Data. With an interval of a short first time Δt (about several microseconds to tens of microseconds, equivalent to several percent of the display period) after the charging connection signal is finished, a shared connection signal is provided by the shared gate line GS, such that the low-voltage pixel electrode 11 shares charges with the first shared capacitor CS1, the voltage on the low-voltage pixel electrode 11 is reduced (because of polarity reversion, the polarity of charges in the low-voltage pixel electrode 11 and the first shared capacitor CS1 are reverse). Of course, above is only one example for the CS-SPVA mode liquid crystal display device, the circuit structure, number of pixel electrodes, number of the orientation domains of each pixel electrode may be altered.
Note that the “voltage” mentioned in the liquid crystal display refers to the voltage for driving the liquid crystal pixel unit, “high voltage” and “low voltage” for the pixel electrodes are not absolute voltage values (in other words, are not compared to ground), but refer to an absolute value of the difference between the pixel electrode voltage and a common electrode voltage. The larger the absolute value of the difference between the pixel electrode voltage and the common electrode voltage (the former may be larger or lower than the latter), the higher the pixel electrode voltage, otherwise the pixel electrode voltage may be lower. The “polarity” of voltage is also not compared to the ground voltage, but to the common electrode voltage. For example, “the pixel electrode voltage and the shared capacitor voltage have opposite polarities”, means that one of the pixel electrode voltage and the shared capacitor voltage is larger than the common electrode voltage, and the other is lower than the common electrode voltage.
While the existing liquid crystal display device of CS-SPVA mode can achieve the effect of a plurality of domains, but the number of domains is still insufficient; meanwhile, due to limits of manufacturing process and the like, there may be errors in the capacitance values of the storage capacitor and the shared capacitor of the liquid crystal display device, which will cause inaccurate voltage on the pixel electrode, and has impact on display quality.